1. Field of the Invention
This invention relates in general to fluid control valves, such as used in oilfield workover applications and in particular to a plug valve having a metal-to-metal seal between a rotatable plug and a sealing segments.
2. Description of the Prior Art
In fluid control valves of the plug type, a rotatable, cylindrical plug with a transverse hole is mounted in a transverse opening of the fluid flow valve body. The rotation of the plug is achieved through the use of a rotatable stem, which allows the valve to move between a closed position, in which the plug valve prevents fluid flow through the flow passage, and an open position, in which the plug valve allows the fluid to flow.
The plug is sealed by a pair of semi-cylindrical segments, which are placed in recesses formed between the transverse opening and the flow passages. Each segment has a hole that registers with one of the flow passages and is located between the plug valve and one of the flow passages. A metal-to-metal seal is formed between the inner side of each segment and the plug. An elastomeric seal seals the outer side of each segment to the recess and exerts an inward force on the segment to cause the metal-to-metal sealing. The practice, however, has proven to be as much an art as it is a science because the segments must be formed nearly perfectly in order to sufficiently form a metal-to-metal seal. Because of tolerances, the plug may shift slightly from the open to the closed position. As such, manufacturers must spend extra time and money to achieve an exact fit.